The world knows Japan for its fast, clean, and efficient transport services. You need only think of the Shinkansen, perhaps better known as bullet trains, to prove this point. But there is one construction project which plagues the country.
Japan built Kansai International Airport on a soft clay seabed beneath an artificial island in Osaka Bay, 5km off the coast of Honshu. In other words, builders lumped the immense weight of an airport on top of a soaked sponge.
And over the past 32 years, the artificial island beneath Kansai has sunk more than 42 feet, pushing the airport ever closer to the sea.
It was constructed to relieve pressure on Japan’s crowded Osaka Airport, and officially opened in 1994.
In some ways, Kansai is a real engineering success. The runways are designed to flex during earthquakes to reduce the risk of damage, and the sinking was expected.
Engineers knew the clay would compress under the weight of such an enormous construction. To control this, developers installed sand drains to channel the trapped water away.
In 2018, Yukako Handa, former communications director for Kansai Airports, told Smithsonian magazine that engineers determined the amount of soil needed to reclaim the land based on ground-level measurements and 50-year subsidence estimates.
Originally these estimates predicted Kansai to sink 13 feet over the 50 years. But just three years into its construction process, and four years before opening, the site had already sunk 27 feet.
The project initially cost roughly £14 billion (US$18.9 billion). Since then, The Independent reported that engineers invested an additional £112 million ($151.6 million) to reinforce the surrounding seawall.
Rate of sinking has slowed. By 2008, the airport was only sinking 2.8 inches a year in comparison to 19 inches a year in 1994. Nonetheless, current forecasts predict that Kansai could drop below sea level by 2056 if it continues sinking at the current rate.
Despite its uncertain future, Kansai International Airport recorded a 109% increase in foreign passengers year-on-year in its November 2025 Traffic Report.
It is also famous for not losing a single piece of baggage across three decades of operation. This incredible achievement has awarded the airport many accolades, including Skytrax’s ‘World’s Best Airport for Baggage Delivery’ in 2024.
While such successes show Kansai in a positive light, its battle against subsidence is far from resolved.
And as Kansai continues to operate under these extraordinary conditions, it stands as both a testament to Japan’s engineering ambition and a reminder of the challenges that come with building against nature.
